A question for the wound experts. :)

How long does it take for a 'blister' to form on a heel?

I am trying to determine if I caused an ulcer on my patient's heel. I came in last night, and at my 10pm assessment, I noticed that the patient's heel had a soft, fluid filled pocket on it. It was not thin blister skin like a burn, but was obviously some sort of breakdown. The heel is very slightly discolored, somewhat darker than her skin.

I almost always float heels on an intubated patient, but she moves a bit and is not my only patient...lol. She was getting turned Q2 nearly on the dot, but she moves her feet and kicks off the heel protectors and slides off the pillows.

Now mind you, this patient has been in the hospital, intubated for 25 days. She is also a CRF patient in fluid overload. (not a dialysis patient) How long do you think it takes? I really hope I didn't do something boneheaded and cause her breakdown.

Next question: Will it definitely turn into an ulcer, or will we be able to prevent it from going any further?

TY in advance